This invention relates to the generation of refrigeration in the course of reducing the pressure of pipeline gas to the pressure of a gas distribution system. More specifically, the invention relates to a process for maximizing the generation of refrigeration when the pressure of pipeline gas is reduced at a pressure letdown control station to supply the gas distribution system.
The pressure of pipeline gas is reduced at many letdown stations merely by isenthalpic expansion, i.e., by passage through a reducing valve. Such pressure reduction is a waste of valuable energy.
Two schemes for utilizing the energy available in pipeline gas at letdown control stations are the generation of electrical energy and the liquefaction of natural gas. To produce electrical energy, the pipeline gas is passed through an expansion turbine which drives an electric generator. U.S. Pat. No. 3,360,944 illustrates a process wherein pipeline natural gas is expanded with the performance of work to produce refrigeration utilized to liquefy a portion of the natural gas.
Depending on the location of each letdown control station, the generation of electric energy or the production of liquefied natural gas may not be economically attractive. In such case, the conversion of the energy available in the pipline gas reaching the letdown station to bulk, low-cost refrigeration may be a preferred and valuable alternative particularly where local industries require refrigeration. The frozen food industry, suppliers of ice and manufacturers of dry ice are examples of industries which consume large quantities of refrigeration.
Accordingly, a principal object of this invention is to convert expansion energy as derived from pipeline gas to low-cost refrigeration.
Another important object is to maximize the generation of refrigeration from the isentropic expansion of the pipeline gas, i.e., expansion with the performance of work.
These and other objects and advantages of the invention will be evident from the description which follows.